Table 1 baseline characteristics

Age (mean ± SD, years)

66.48 ± 16.7

Genders Male (n/%)

38/61

Body mass index (mean ± SD, kg/m²)

22.5 ± 6.3

Medical patients (n/%)

42/68

Surgical patients (n/%)

20/32

APACHE II score (mean ± SD)

18.5 ± 7.2

 Hypertension

35/57

 Diabetes

21/34

 Chronic kidney disease

18/29

 Ischemic heart disease

14/23

 COPD

6/10

 Hypothyroid

5/8

 Adrenal insufficiency

3/5

 Asthma

2/3

 Neurological disease

10/16

 Septic shock

10/16

 Pneumonia

8/13

 Heart disease

8/13

 COPD exacerbation

4/7

 Post-operative conditions

21/34

 Sodium (mmol/L)

135.9 ± 5.2

 Potassium (mmol/L)

3.9 ± 0.59

 Bicarbonate (mmol/L)

23.6 ± 4.5

 Calcium (mmol/L)

7.9 ± 0.65

 Magnesium (mmol/L)

1.97 ± 0.37

 Phosphate (mmol/L)

4.6 ± 5.4

 Albumin (g/dl)

24.8 ± 5.6

 BUN (mg/dl)

29.3 ± 23.9

 Creatinine (mg/dl)

1.9 ± 2.3

 Hematocrit (%)

31.8 ± 5.5

Vital capacity (mean ± SD, L)

0.97 ± 0.4

Tidal volume (mean ± SD, L)

0.41 ± 0.2

PI_MAX (mean ± SD, mmHg)

40.7 ± 16.4

RSBI (mean ± SD, breath•min^− 1/L)

60.2 ± 33.1

Duration of mechanical ventilation(days) ^a

2.8(1.1–5.7)

Length of stay (days)

 Intensive care stay^a

4.8 (2.9–9.6)

 Hospital stay^a

13.3 (7.8–25.9)